This investigation will be concerned with the mechanism of hydrolysis of acetals and acetal analogues in the attempt to gain information regarding the chemical possibilities by which glycosidases might be acting. Differences in the non-enzymatic hydrolysis of acetals and the enzymatic hydrolysis of glycosides indicate that the enzymes are using mechanisms to which there are few analogies in organic chemistry. It will be the purpose of this investigation to dem nstrate some of the mechanistic possibilities in non-enzymatic systems. It will also be the purpose of this investigation to elucidate more completely the mechanisms of action of lysozyme. The mechanisms of hydrolysis of a series of substituted imidazolidines and their respective cationic Schiff-bases will be determined to further understanding of the reactions of N5,N10-methylene tetrahydrofolic acid. In particular we will attempt to find general acid catalysis in the hydrolytic reactions since it is likely that such catalysis takes place in the cofactor reactions. The effect on mechanism of systematically varying nitrogen basicity and carbonium ion stability will be determined. A series of derivatives of tetrahydrofolic acid will be prepared to investigate nonenzymatic hydrolysis and to determine the specificity requirements of thymidylate synthetase.